The media of magneto-optical disks, optical disks, phase change disks, and the like are known as digital disks. The recording and reproduction of the disk are all carried out by data transfer in AC coupling. This means that it is difficult to record/reproduce signal components of the low frequency region at high efficiency with respect to data recorded at high density on a digital disk.
It is therefore necessary to carry out modulation that suppresses the direct current and low frequency components for recording data. The recorded data stream includes the clock frequency components of recording. At the time of reproduction, the clock frequency components are extracted from the signal of the reproduced data stream. Self clock control is provided that reproduces the reference clock of the reproduction apparatus by the extracted clock frequency component. In modulating digital data, self clock control must be feasible and with few direct current and low frequency components. EFM, 1-7 RLL modulation, 2-7 RLL modulation and the like are known as such modulation systems. RLL-modulated data is NRZI-modulated or NRZ-modulated and recorded on a medium.
Japanese Patent Laying-Open No. 2-96982 proposes a method of preparing a plurality of pseudo random data streams and scrambling the data stream with the pseudo random data that has the smallest DSV (Digital Sum Variation) at the time of recording. Such an adaptive type modulation method that reduces the value of DSV is proposed.
It is known to form a sine wave shape (wobble shape) having a predetermined cycle and amplitude at the wall of a groove in a disk medium. This wobble is well known by those skilled in the art as disclosed in, for example, Japanese Patent Laying-Open No. 7-311962. Address information and the like are recorded in a multiplexed manner by this wobble.